Photographic fixing bath



PHOTOGRAPH-TIC FIXING BATH Marilyn Levy, Red Bank, N.J., assignor to the*United States of America as represented by theSecretary of the 'Army ii No Drawing. Filed Oct. 27, 1960, Ser. No. 65,549 2 Claims. (Cl. 96-61)(Granted under Title 35, US. Code (1952), see. 266) The inventiondescribed herein may be manufactured and used by or for the Governmentfor governmental purposes, without the payment of any royalty thereon.

This invention relates to photographic processing and particularly tothe fixing of photosensitive materials after the image has beendeveloped therein.

In the photographic system wherein silver halide emulsions are used asthe sensitive medium after development the residual unexposed halidemust be completely removed. This is accomplished by bathing in asolution of sodium thiosulphate until all of the halide is removed. Toinsure that this operation is complete and to protect the delicatewetted emulsion certain other ingredients may be added, for example, asmall quantity of acid such as acetic acid neutralizes the alkalicarried by the emulsion from the developer. A hardener also is addedsuch as potassium alum and a preservative such as sodium sulphite.

In the use of such fixing baths the undeveloped silver halide grains aredissolved and removed from the emulsion. Since thiosulphate ions convertto the silver thiosulphate complex in a fixing bath, the activity of thebath becomes diminished with constant use. The formulation of sodiumiodide as a result of the conversion of silver iodide to silverthiosulfate complex also reduces the rate of fixation. If the bath isused too long it may lose its ability to remove all of the unused silversalts from the emulsion. These unused salts in time will decompose andstain the negative or print.

This progressive consumption of activity of the fixing bath has manydisadvantages. It may lead to unstable and inferior end results due tothe dificulty in determining when to discard the bath or it may resultin setting up a safety factor which requires discarding the bath beforeits useful activity is consumed.

The invention adds an ingredient to the fixing bath which controls thebath activity and prolongs the life of the bath. By so doing thequantity of chemicals consumed is reduced. The practice of thisinvention also provides means for maintaining quality control of the endproducts which has not heretofore been readily achievable.

By adding a suitable quantity, of colloidal silica to the fixing bathits active life will be greatly prolonged. The

silica which is thoroughly dispersed in the bath acts to neutralize thedeterrent effect of accumulated silver salts in the bath. Thus the bathcontinues to function for a long period after the same bath without theadditive would have ceased to be effective.

Since the coloidal silica immediately becomes effective in the presenceof dissolved silver salts its corrective function maintains fullactivity of the fixing bath thruout the processing of large quantitiesof sensitive materials.

Processing with the bath of the invention insures consistent highquality results as well as greatly extended area United States Patentupon this determination.

3,170,793 Patented Feb. 23, 1965 of sensitive material processedcomparedwith conventional fixing baths. Colloidal silica as an additivehas been found to be particularly successful in increasing the capacityof fixing baths and has the added property of being chemically neutralto the other bath ingredients. The silica functions only to absorb andotherwise render the accumulated salts in the bath ineffective inslowing the fixing potential of the bath.

The invention in its broad aspect includes fixing baths having anydesired composition of chemicals including sodium thiosulphate as themain dissolving agent for the undeveloped silver halide in the sensitiveemulsion. The hypo may be used alone or with various proportions ofcontrol chemicals such as acetic acid, sodium sulphite and a hardenersuch as potassium alum.

Into the above suggested compositions a quantity of colloidal silica isdispersed to constitute the formulation of the invention.

An example of a formulation embodying the invention is as follows:

The above composition or a similar one including the proper amount ofcoloidal silica is used after the film or print has been exposed,developed and desirably immersed in an acidic stop bath. The developedmaterial is immersed in the fixing bath for the usual time of from 10 to20 minutes for films and 5 to 10 minutes for prints. During suchimmersion the conventional degree of agitation should be carried out.The processed material is then washed and dried in the usual manner.

It has been found that in the bath of the invention an accurate andconsistent determination may be made of its total fixing capacity eitherby trial or in some other manner. Subsequent fixing operations can thenbe based Knowing their potentiality the baths may be used up to theirfull capacity Without fear of forcing them beyond the safety point. Thismeans that full benefit may be derived from the added fixing capacitywhich the invention imparts to the bath.

A further feature of the invention is its adaptation to baths havingincreased viscosity which is a valuable attribute under certainenvironmental conditions. For example there are military operationswhich require that photographic processing to be carried out in flightor in moving vehicles where vibration and erratic bodily movements ofsolution containers disrupt open tray operations. It has been found thatsolutions of increased viscosity may successfully be used under suchconditions.

The properties of the present invention may readily be extended toinclude such increased viscosity solutions. If the addition of a normalamount of silica suflices to extend the capacity of the bath fails toproduce the required Viscosity more silica may be added until therequired immobility of the solution is achieved. The bath having theadded silica will also function with the required effectiveness toextend the fixing capacity thereof.

What is claimed is:

1. A fixing bath comprising the following ingredients:

Water liter 1 Sodium thiosulphate grams 50 to 300 Sodium sulphite(desiccated) do 5 to 30 Acetic acid 28% cc to 100 Potassium alum grams 5to 30 Boric acid crystals do 3 to Colloidal silica dispersed in thesolution do 5 to 300 2. A fixing bath comprising an aqueous solution ofsodium thiosulphate in the proportion of 50 to 300 grams per liter ofWater, a quantity of preservative, a quantity of gelatine hardeningagent, an acidifying agent in quantity to change the pH value of thebath less than 5%, the

4 quantity of preservative and hardening agent having a total weightless than /3 to A of the weight of sodium thiosulphate and a quantity ofcoloidal silica in an amount from to 250 grams per liter.

References Cited by the Examiner UNITED STATES PATENTS 2,616,807 11/52Land 9661 X 2,871,121 1/59 Kimura 9661 OTHER REFERENCES Photo Lab Index,Section 2, page 17, Quarterly Supplement No. (New Page), Morgan andLester, New York.

NORMAN TORCHIN, Primary Examiner.

MILTON STERMAN, LOUIS P. QUAST, Examiners.

2. A FIXING BATH COMPRISING AN AQUEOUS SOLUTION OF SODIUM THIOSULPHATEIN THE PROPORTION OF 50 TO 300 GRAMS PER LITER OF WATER, A QUANTITY OFPRESERVATIVE, A QUANTITY OF GELATINE HARDENING AGENT, AN ACIDIFYINGAGENT IN QUANTITY TO CHANGE THE PH VALUE OF THE BATH LESS THAN 5%, THEQUANTITY OF PRESERVATIVE AND HARDENING AGENT HAVING A TOTAL WEIGHT LESSTHAN 1/3 TO 1/4 OF THE WEIGHT OF SODIUM THIOSULPHATE AND A QUANTITY OFCOLOIDAL SILICA IN AN AMOUNT FROM 20 TO 250 GRAMS PER LITER.